Assembly for Mixing a Medium with the Exhaust Gas Flow of a Motor Vehicle Exhaust System

ABSTRACT

An assembly for mixing a medium with an exhaust gas flow of a motor vehicle exhaust system has a first exhaust pipe and a second exhaust pipe. The first exhaust pipe comprises a device for introducing the medium and opens axially into a connecting member that is widened with respect to the first exhaust pipe. The second exhaust pipe opens laterally into the connecting member. The connecting member is configured to impart an angular momentum to the exhaust gas flow.

RELATED APPLICATIONS

The application is the U.S. National Phase of PCT/EP2007/003004 filed Apr. 3, 2007, which claimed priority to German Application 10 2006 015 964.0 filed Apr. 5, 2006.

BACKGROUND OF THE INVENTION

The invention relates to an assembly for mixing a medium with the exhaust gas flow of a motor vehicle exhaust system.

In modern exhaust systems, it is sometimes necessary to introduce a medium into the exhaust gas flow to generate specific reactions. For example, it is possible to inject urea in a dissolved form upstream of a selective catalytic reduction (SCR) catalytic converter to provide ammonia as a reducing agent for the nitrogen oxides present in the exhaust gas. It is also possible to supply a reducing agent, such as fuel, upstream of a particulate filter to burn off the particulates retained in the filter in a controlled way. Generally, it has to be taken into consideration that the medium which is to be introduced has to be distributed as homogeneously as possible in the exhaust gas flow to generate a uniform effect.

This also particularly applies to two-branch exhaust systems, such as those for a 6 or 8-cylinder engine for example, where only one urea injection device is typically provided for SCR applications in order to reduce costs. The injection device is then usually arranged downstream of a connecting member which merges the exhaust gas flows from the two exhaust pipes. The problem of obtaining an intensive mixing of the exhaust gas with the introduced medium also arises with this configuration.

It is therefore the object of the invention to obtain a uniform distribution of an introduced medium in the exhaust gas flow, in particular in the exhaust gas flow of a two-branch exhaust system, with a low effort and a high reliability.

SUMMARY OF THE INVENTION

The invention provides an assembly of the type initially mentioned, which has a first exhaust pipe and a second exhaust pipe. The first exhaust pipe comprises a device for introducing the medium and opens axially into a connecting member that is widened with respect to the first exhaust pipe. The second exhaust pipe opens laterally into the connecting member. The connecting member is configured to impart an angular momentum to the exhaust gas flow. The medium is thus first supplied to the exhaust gas flow in the first exhaust pipe and enters, along with this exhaust gas flow, the connecting member in which a mixing with an exhaust gas flow from the second exhaust pipe is produced. A spin leading to a good swirl, and therefore to a good distribution of the medium, is imparted to the entire exhaust gas flow inside the connecting member. Furthermore, soiling of pipe walls by the medium, for example by a settling of the medium at the pipe walls, is avoided. The configuration according to the invention is particularly suitable for a two-branch exhaust system, with only a single device for introducing the medium being necessary, but the configuration can be used in any exhaust system where the exhaust gas flow is distributed at least partially to two pipes.

The first exhaust pipe extends beyond an opening region of the second exhaust pipe into an interior of the connecting member. The exhaust gas flow from the second exhaust pipe thus first strikes a wall of the first exhaust pipe and is then forced into a rotary movement about an end of the first exhaust pipe.

The connecting member has a cone shape with the first exhaust pipe opening into a larger end face of the connecting member. A particularly good swirl of the exhaust gas flow is obtained due to the obliquely tapering lateral walls of the connecting member.

Advantageously, the second exhaust pipe opens tangentially into the connecting member. The exhaust gas flow from the second exhaust pipe is therefore forced in a simple way to a helical path along the inner wall of the connecting member.

To support the swirl of the exhaust gas flow, the connecting member may have on an inner side a guiding face for the exhaust gas flow.

To facilitate the mixing of the introduced medium with the exhaust gas flow in the first exhaust pipe, the device may be arranged downstream of a directing member in the first exhaust pipe.

According to a one example embodiment, the second exhaust pipe is formed in one piece with the connecting member.

As already mentioned initially, the device may be a urea injection device. However, the device could also be a device for introducing a reducing agent such as fuel for the regeneration of a particulate filter, for example.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will be apparent from the description below of a preferred embodiment with reference to the enclosed drawings.

FIG. 1 shows a longitudinal section through an assembly according to the invention; and

FIG. 2 shows a cross-section through the assembly along the line II-II.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows an assembly 10 which is arranged in an exhaust system of a motor vehicle (not shown) and has a first exhaust pipe 12 and a second exhaust pipe 14, with exhaust gas flowing through each exhaust pipe in the direction of the arrows P₁. The exhaust gases flow from the first and second exhaust pipes 12, 14 and are merged in a connecting member 16. The second exhaust pipe 14 opens laterally, in particular tangentially (cf. FIG. 2), into the connecting member 16 and is formed in one piece with the connecting member 16 in the example shown.

The first exhaust pipe 12 opens axially into the connecting member 16 and has a device 18 for introducing a medium, which in the present case comprises a urea injection device that is arranged downstream of a directing member 20. The connecting member 16 has the shape of a cone and is widened with respect to the first exhaust pipe 12 which extends beyond the opening region of the second exhaust pipe 14 into the interior of the connecting member 16.

Due to the tangential introduction of the exhaust gas flow from the second exhaust pipe 14 into the cone-shaped connecting member 16, a swirl of the united exhaust gas flow is obtained. This swirl is also referred to as a Vortex and leads to a particularly good mixing with the introduced medium (in the present case dissolved urea). In the figures, the swirl is indicated by the helically extending arrow P₂.

Unlike the embodiment illustrated, the connecting member 16 may have on its inner side a guiding face for the exhaust gas flow, which is formed by a guide plate or by plastically deformed wall portions of the connecting member, for example.

Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention. 

1. An assembly for mixing a medium with an exhaust gas flow of a motor vehicle exhaust system, comprising: a first exhaust pipe comprising a device for introducing a medium into an exhaust gas flow, the first exhaust pipe opening axially into a connecting member that is widened with respect to the first exhaust pipe; and a second exhaust pipe that opens laterally into the connecting member, wherein connecting member is configured to impart an angular momentum to the exhaust gas flow.
 2. The assembly according to claim 1, wherein the first exhaust pipe extends beyond an opening region of the second exhaust pipe into an interior of the connecting member.
 3. The assembly according to claim 1, wherein the connecting member has a cone shape.
 4. The assembly according to claim 1, wherein the second exhaust pipe opens tangentially into the connecting member.
 5. The assembly according to claim 1, wherein an inner side of the connecting member has a guiding face for the exhaust gas flow.
 6. The assembly according to claim 1, wherein the device is arranged downstream of a directing member in the first exhaust pipe.
 7. The assembly according to claim 1, wherein the second exhaust pipe is formed in one piece with the connecting member.
 8. The assembly according to claim 1, wherein the device is a urea injection device. 